Miners in the nation’s largest coal-producing region are leaving more of the fossil fuel in the ground as prices fall for alternatives, including natural gas, and demand erodes from power-generation customers.

Coal production from the Powder River Basin, an arid region spread over parts of Wyoming and Montana that produces about 40 percent of all U.S. coal, has declined by one-third between 2008 and 2017. It is expected to continue to drop in 2019. That has prompted many mining companies in the region to cut staff or benefits, reduce their exposure to the basin or leave it entirely.

“We’ve seen in the last few years, especially with the amount of gas coming online and fuel switching, that’s biting into our customer base,” said Travis Deti, executive director of the Wyoming Mining Association. “That remains a concern for the future.”

The Powder River Basin is expected to produce 338 million tons of coal in 2018, but that total is projected to fall to 329 million tons in 2019, according to a December report from Seaport Global analyst Mark Levin. Coal analyst John Hanou, of Hanou Energy Consulting LLC, expects a weaker performance and is predicting Powder River Basin production will drop to 315 million tons in 2019.

The drop in demand is expected despite the Trump administration’s efforts to boost the coal industry by easing regulations. President Donald Trump had made assisting miners a centerpiece of his 2016 presidential campaign, and this past August declared the industry was back.

Companies in 2017 extracted about 334 million tons of coal in the basin, where excavators scrape coal from rich seams in walls of earth. That was the second-lowest level in about two decades, though up from 314 million tons in 2016, according to federal data.

Cloud Peak Energy Inc., the third-largest producer in the basin, said in November it is considering a sale as a result of declines in the coal market. Cost-saving moves for Cloud Peak, formed nearly a decade ago after being spun off from miner Rio Tinto PLC, have included ending a medical plan for retirees and seeking a buyer for its former main office in Gillette, Wyo.

In 2017, Contura Energy Inc. exited the region, selling two mines to Blackjewel LLC, a closely held venture led by a Virginia-based mining executive.

Peabody Energy Corp., the region’s largest miner, has sought to relinquish Powder River Basin acreage, a move that moderates its exposure to the market for thermal coal, used in power plants. It recently bought a mine in Alabama that offers metallurgical coal, used in steelmaking.

The region remains a core area for Peabody, as it offers coal that is among the most competitive with natural gas, a spokesman for the company said. But the miner has focused the vast majority of its investments on seaborne metallurgical-coal resources, he said.

A train hauls coal mined in the Powder River Basin. The basin is the largest coal-producing region in the U.S.

THE ASSOCIATED PRESS